This invention relates generally to registration systems and particularly to registration systems useful in connection with the manufacture of cathode ray tubes (CRTs) characterized by a flat panel and a shadow mask consisting of a thin, tensed foil.
The shadow mask type of color picture tube has given statisfactory performance for many years. The shadow mask used in such picture tubes is generally spherical, self supporting and, of necessity, has substantial thickness. In the above-mentioned copending applications a different type of color tube construction is described. In the disclosed constructions, a flat glass panel faceplate has a tensed foil mask maintained in close registration thereto for selectively shadowing elemental ones of a plurality of triads of colored light-emitting phosphors deposited in an ordered pattern on the inner surface of the panel. The mosaic of elemental phosphors, called the target or screen, is generally formed by a photodeposition process utilizing the shadow mask and a light source that simulates the electron beam in the CRT. The assemblage is removably positioned in precise alignment through the use of registration means formed in each of the panel seal land, the seal land of the frame that supports the shadow mask and the seal end of the tube funnel. Precise registration is required during screening of the target of the faceplate. In a well-known screening process each pattern of different colored light emitting phosphors and a "black surround" or grille requires precise repositioning of the mask. Thus the need for an accurate registration system is paramount.
The above mentioned Strauss patent describes a ball and two-groove registration system system for a flat panel CRT. There, three radially disposed V-sided grooves are formed in the panel seal land in a confronting relation with three similar radially disposed V-sided grooves formed in the frame seal land. The so-called "Q" spacing between the tensed mask and the phosphor target on the panel is maintained by three balls of given diameter and sphericity, each co-pending with one of the pairs of grooves. The balls and grooves provide a minimum friction kinematic mount for repeatedly returning the mask and panel to the same geometric orientation with respect to each other. As those skilled in the art will readily perceive, the balls may occupy an "infinite" number of positions along their grooves and still retain the appropriate geometric registration required. The essential teaching of the Strauss patent is to permit the balls the freedom to roll to minimize friction and maximize the opportunity for the frame and panel, and hence the mask and target, to achieve proper registration.
The grooves may be formed in the glass pieces by any number of techniques, preferably by ultrasonic drilling. Since it is desired to maintain a reseating accuracy of 0.0002 inches, it can readily be appreciated that the need for accurate machining of the grooves in the glass pieces cannot be overemphasized. Imperfections in the sidewalls of the grooves may result in a change in the "Q" distance between the mask and target, causing misregistration between the phosphor target and the mask. Since the target is formed by a screening process using the mask as an exposure element, sidewall inaccuracies may be tolerated if they are consistently repeated. Since repeatability of registration is essential, it is highly desirable to provide a system wherein the balls would be assured of rolling movement and yet be restricted in their range of travel so as to relax the requirements on imperfections in the groove sidewalls.